Witnesses described seeing the student "walking, staggering and zig-zagging" before standing "dangerously" close to the cliff edge moments before he fell.

Arthur and a friend - who cannot be named for legal reasons - had earlier taken LSD, also known as acid, an inquest in Brighton heard.

Members of the public tried to resuscitate him after he was found lying on the underpass of Ovingdean Gap without any shoes or socks, but he died later at Royal Sussex County Hospital.

Veronica Hamilton-Deeley, senior coroner for Brighton, recorded a conclusion of accidental death.

She said: "I expect the decision and planning to take LSD, or a hallucinogenic drug likely to be LSD, was made on the spur of the moment.

"It's clear he could not know what was real and what was not real. It's completely impossible to know what was in Arthur's mind and what he was seeing."

Cave and his wife Susie briefly walked out of the courtroom before graphic details of their son's injuries were read out from a post-mortem examination report. The coroner said the cause of death was "unsurvivable head injuries due to a witnessed fall from a cliff".

A contributory factor was the recent ingestion of a hallucinogenic drug.

The boy who took LSD with Arthur said he researched online about the effects of the drug but had not read anything about the "darker side".

The pair had arranged to take the drug on a grassy area near Rottingdean Windmill in Brighton.

In a summary of the boy's statement, Detective Constable Vicky Loft the court: "Arthur was hesitant but said if they were worrying about things it would have an effect on the trip and make it a more negative experience.

"They decided to take one together at the same time. They took a tablet each, placed it on their tongue and waited for the effects to start."

The boy said he and Arthur took three tablets between them and they were initially in "good spirits and happy", but he then started having "vivid hallucinations", including seeing patches of oil on the grass and shapes and colours in the sky.

Dc Loft said: "(The boy) became paranoid and felt like people were staring at him in cars. He couldn't tell what was real and what was not real.

"He thought he could see Arthur covered in vomit but wasn't sure if it was real."

The boy said he was not sure if he and Arthur walked off together but he recalled they went their "separate ways".

Another boy, who cannot be named for legal reasons, said Arthur had face-timed him and seemed in "good spirits" before he sent messages on social media saying the drugs were taking effect.

During the inquest, clinical scientist Amber Crampton said there was evidence that LSD had seen a resurgence in popularity.

She told the court: "I don't imagine it's too difficult to get hold of in Brighton.

"It used to be popular in the 60s and 70s. It's more popular now than many people are aware."

Cave, who clutched a tissue during the inquest, hugged his wife after the hearing. Dressed in a black suit, white shirt and tie, the Australian musician - best known as lead singer of Nick Cave and the Bad Seeds - made no comment as he left the court building.

In a statement issued after the inquest, the Cave family thanked the coroner, medics who treated Arthur and the members of the public who helped at the scene.

They said: "We have been overwhelmed by the many messages of support we have received from the people of Brighton and beyond, and the kindness they have shown to us.

"Arthur was a wonderfully unruly, creative and free-spirited young man with an infectious, happy, funny daredevil nature.

"He loved his friends and family, idolised his twin brother Earl and was never far from his side. And we loved him back - to his core - and we miss him deeply."